If set up `rubygems: latest` in workflow,
it will cause the error with Ruby 3.0 because the latest rubygems does not support Ruby 3.0.
Ref. https://rubygems.org/gems/rubygems-update
### Error message
```
Updating RubyGems
/opt/hostedtoolcache/Ruby/3.0.7/x64/bin/gem --version
3.2.33
Default RubyGems version is 3.2.33
Updating RubyGems to latest version
/opt/hostedtoolcache/Ruby/3.0.7/x64/bin/gem update --system
ERROR: Error installing rubygems-update:
rubygems-update-3.6.1 requires Ruby version >= 3.1.0. The current ruby version is 3.0.7.220.
ERROR: While executing gem ... (NoMethodError)
undefined method `version' for nil:NilClass
Updating rubygems-update
Took 2.86 seconds
Error: The process '/opt/hostedtoolcache/Ruby/3.0.7/x64/bin/gem' failed with exit code 1
```
### How to reproduce
```
uses: ruby/setup-ruby@v1
with:
ruby-version: "3.0"
rubygems: latest
```
